Damming eutrophication leads to cyanobacteria blooms degrading drinking water quality, posing a significant challenge to water resource management and public health. The aim of this article is to investigate the spatio-temporal variation and the influence of physico-chemical parameters on Microcystis blooms and microcystin content in the Cheffia DAM at El Tarf (north-east Algeria), and to define recommendations for the water quality of this DAM. A bimonthly sampling campaign was conducted from January to June. Samples were collected from five depths (0, -5, 10, -15, -20 meters). At each sampling point, two samples were taken: for physicochemical analysis and for chlorophyll-a and cyanotoxin determination. The enzyme-linked immunosorbent assay (ELISA) was used to determine microcystin contents.The results showed that temperature and pH were the main factors positively influencing Microcystis proliferation and toxin levels. Orthophosphates were the only nutrient showing a negative correlation with cell density, and Chlorophyll-a was directly correlated with Microcystis abundance and toxicity. In conclusion, the results highlight the influence of environmental conditions, especially temperature and pH, on the blooms of Microcystis populations and microcystin concentrations. Understanding the interactions between these factors is essential for predicting and managing harmful algal blooms in drinking water DAMS and aquatic ecosystems.